Kp index explained - what Kp you need to see the northern lights

The Kp index explained: how strong a storm you need to see the aurora

Seeing the northern lights far from the Arctic is not luck, it is a question of storm strength and a dark sky. In Edinburgh Kp 3 can be enough, in London you need about 5.5, in New York about 7.5. Here is what those numbers mean and how not to miss the next chance.

Marcin FierkaPublished: October 1, 2026

Why the aurora sometimes reaches further south

The aurora appears when charged particles from the Sun hit the upper atmosphere. Most of the time this happens in an oval around the magnetic pole, over Scandinavia, Iceland, Canada and Alaska. When the Sun throws a large cloud of plasma towards Earth, the magnetic field gets shaken hard and the aurora oval expands towards the equator. That is when people in London, Berlin or Seattle get their chance.

The strength of that disturbance is measured by the Kp index.

The Kp index in short

Kp runs from 0 to 9. At 0 to 3 the magnetic field is quiet, from 5 upwards it is a geomagnetic storm. The US space weather agency NOAA splits storms into five levels:

Kp	Storm level	What it means for the aurora
5	G1, minor	aurora common at high latitudes
6	G2, moderate	seen down to about 55° geomagnetic latitude
7	G3, strong	seen down to about 50° geomagnetic latitude
8	G4, severe	seen down to about 45° geomagnetic latitude
9	G5, extreme	seen down to about 40° geomagnetic latitude

Geomagnetic latitude is not the same as the latitude on a map. The magnetic pole sits over northern Canada, so North America is “closer” to the aurora than Europe at the same latitude. That is why Seattle needs a lower Kp than Paris, even though they lie at a similar latitude.

What Kp your city needs

Zenitmap estimates for the aurora to appear low on the northern horizon:

Edinburgh: about Kp 3,
London, Amsterdam, Seattle, Minneapolis: about Kp 5.5,
Berlin, Toronto: about Kp 6,
Chicago: about Kp 7,
New York: about Kp 7.5.

For your own city check the Aurora tonight page, where we show the live Kp next to the value each city needs.

How to read the forecast

NOAA publishes a three-day Kp forecast, which you can see on our aurora page together with the current Kp and the live aurora oval. A few rules that save a lot of disappointment:

Forecasts are uncertain. A plasma cloud takes one to three days to reach Earth, and its real strength only shows when it arrives. A forecast of Kp 7 can end up as 5 or grow to 8.
Only the night counts. A high Kp at noon does nothing for you. Check whether the high values fall in your local night.
Clouds cancel everything. Even at Kp 8 you will see nothing under an overcast sky. Look at the live cloud map.
The Moon gets in the way. Around full moon a faint aurora disappears in the bright sky. Today’s Moon phase is on Sky tonight.

Where and how to look

Get out of town. Street lights wash out a faint aurora. Even 10 to 20 km from a large city makes a difference.
Find an open view to the north. A coast, fields, a lake or a hill. Away from the Arctic the aurora usually stays low on the horizon.
Give your eyes 20 minutes. Night vision builds up gradually. Do not look at a bright phone screen in the meantime.
Take a photo with your phone. Night mode with a few seconds of exposure shows colours the eye cannot see yet. Often the photo is the first sign that the aurora is already there.
Be patient. The aurora comes in waves. A quiet sky can turn into bright pillars within minutes.

The biggest aurora in years

On 10-11 May 2024 a storm of the highest level, G5 or Kp 9, reached Earth. According to USGS the previous G5 storm happened on 31 October 2003. The aurora was photographed across much of Europe and North America, far south of where it is normally seen.

Nights like that are rare, but in October 2024 NASA and NOAA announced that the Sun had entered the maximum period of its 11-year cycle. During this period strong geomagnetic storms happen more often than usual, so it pays to keep an eye on the forecast.

FAQ

What Kp do I need to see the northern lights?

It depends on your geomagnetic latitude. By our estimates the aurora can appear low on the northern horizon at about Kp 3 in Edinburgh, 5.5 in London, Amsterdam, Seattle and Minneapolis, 6 in Berlin and Toronto, 7 in Chicago and 7.5 in New York. At Kp 9 it can be seen much further south.

What do G1 to G5 mean?

They are NOAA storm levels. G1 corresponds to Kp 5, G2 to Kp 6, G3 to Kp 7, G4 to Kp 8 and G5, the extreme level, to Kp 9.

When was the last G5 storm?

On 10-11 May 2024. According to USGS it was the first G5 storm since 31 October 2003, and the aurora was seen across much of Europe and North America.

Why does the aurora look brighter in photos than to the eye?

A faint aurora looks greyish to the eye, because we see colour poorly in the dark. A camera or a phone in night mode collects light for several seconds and shows the greens and pinks the eye cannot pick up.